1. Field of the Invention
The present invention relates to a display device.
2. Description of the Related Art
Liquid crystal display devices are space-saving, easily portable, and lightweight display devices with low power dissipation, and are extensively used today as displays for notebook computers, TV sets with a reduced thickness and cell phones. Among other things, a super twisted nematic (STN) mode liquid crystal display device has found applications in a broad variety of electronic appliances including cell phones. This is because an STN mode liquid crystal display device has a relatively simple structure and is less expensive.
FIG. 13 is a perspective view schematically illustrating the structure of a conventional STN mode liquid crystal display device. As shown in FIG. 13, the STN mode liquid crystal display device includes two substrates 100 and 102 that face each other and a liquid crystal layer 104 interposed between these substrates 100 and 102. On one surface of one substrate 100, multiple striped common lines 106 are provided so as to face the liquid crystal layer 104. On one surface of the other substrate 102, multiple striped segment lines 108 are provided so as to face the liquid crystal layer 104, too. The direction in which the segment lines 108 extend is perpendicular to the direction in which the common lines 106 extend. In this STN mode liquid crystal display device, when a voltage is created between one common line 106 and one segment line 108, a portion of the liquid crystal layer 104, located at the intersection between these lines 106 and 108, is driven by the voltage applied thereto. These common and segment lines 106 and 108 also function as pixel electrodes and are made of a transparent conductive film such as an ITO film.
However, this STN mode liquid crystal display device has no active components as switching elements. Accordingly, the voltage to be applied to the liquid crystal layer is inconstant (i.e., the voltage applied cannot be retained constantly enough). For that reason, a liquid crystal display device of this type cannot fully satisfy various requirements including multi-gray-scale display (in 4,096 or 6,500 colors, for example), high resolution and high contrast ratio.
Thus, a modified STN mode liquid crystal display device, in which active components are provided for respective pixels, was proposed. In a liquid crystal display device of this newly proposed type, a data signal is supplied to one of striped data electrodes on a counter substrate, and a reference signal voltage (i.e., a common voltage) is applied to a pixel electrode that is connected to its associated switching element. This type of liquid crystal display device will be referred to herein as a xe2x80x9cdata-to-counter-electrodexe2x80x9d type liquid crystal display device. A liquid crystal display device of this type is disclosed in U.S. Pat. No. 4,694,287, for example. Hereinafter, the data-to-counter-electrode type liquid crystal display device disclosed in the United States patent identified above will be described with reference to FIG. 14.
As shown in FIG. 14, multiple three-terminal switching elements (i.e., TFTs) 112 and pixel electrodes 114 are arranged in columns and rows (i.e., in matrix), and multiple gate lines 116 and multiple reference signal lines 118 are arranged in the row direction, on one surface of one substrate 110 so as to face a liquid crystal layer. The three terminals of each TFT 112 are connected to its associated pixel electrode 114, gate line 116 and reference signal line 118, respectively. In response to a gate signal that has been supplied to the gate electrode of a TFT 112 through its associated gate line 116, the TFT 112 is turned ON. Then, a reference signal voltage (i.e., common voltage) is applied through its associated reference signal line 118 to its associated pixel electrode 114 by way of the TFT 112 in ON state.
On the surface of the counter substrate 120, multiple striped data electrodes 122 are provided so as to face the liquid crystal layer and cross the gate lines 116 and reference signal lines 118 substantially at right angles when this device is viewed from above. A data (or video) signal is supplied to each of these data electrodes 122. A portion 124 of each data electrode 122 that faces its associated pixel electrode 114 also functions as a counter electrode.
Generally speaking, very precise processing on the order of several microns is required to fabricate a liquid crystal display device. Thus, if dust is deposited on, or a tiny scratch is done on, a liquid crystal display device being fabricated, then current leakage or disconnection is likely caused in the final product. Recently, a liquid crystal display device needs to increase the number of colors to display or its resolution and minimize the non-display area around its periphery. Accordingly, it is often necessary to pattern a conductive film into a desired shape on a color filter layer, an overcoat resin or a stepped portion. The interconnects of a liquid crystal display device also need to decrease their widths. Under the circumstances such as these, the current leakage, disconnection and other defects happen more and more often, which is a major factor of unwanted decrease in production yield.
To overcome these problems, Japanese Laid-Open Publication No. 3-85525, for example, discloses an active-matrix-addressed liquid crystal display device including a spare line to repair a disconnection.
In the liquid crystal display device disclosed in the publication identified above, the spare line to repair a disconnected source or gate line is provided on an active-matrix substrate. That is to say, the spare line and the line to be repaired are located on the same substrate.
In the data-to-counter-electrode type liquid crystal display device shown in FIG. 14, the striped data electrodes 122 are formed on the counter substrate 120 by patterning a transparent conductive film such as an ITO film. Defects such as disconnection of one of these data electrodes 122 often happen on the counter substrate 120. Thus, to repair such a disconnected data electrode 122, a spare line may be provided as in the active-matrix-addressed liquid crystal display device described above for the substrate 120 including the data electrodes 122.
Hereinafter, such a liquid crystal display device will be described with reference to FIGS. 15A through 15C and FIGS. 16A and 16B. FIGS. 15A and 15B are plan views of the two substrates 120 and 110, respectively. FIG. 15C is transparent plan view of the liquid crystal display device. FIGS. 16A and 16B are partial cross-sectional views of the liquid crystal display device shown in FIG. 15C as taken on the planes XVIaxe2x80x94XVIa and XVIbxe2x80x94XVIb, respectively. Each of the components of this liquid crystal display device, having substantially the same function as the counterpart shown in FIG. 14, will be identified by the same reference numeral and the description thereof will be omitted herein.
In this liquid crystal display device, a spare line 124 to repair any defective data electrode 122 is provided on the substrate 120 on which the data electrodes 122 are located as shown in FIG. 15A. The substrate 120 including the data electrodes 122 and spare line 124 will be referred to herein as a xe2x80x9cfirst substratexe2x80x9d for convenience sake. In this structure, if any of the data electrodes 122 has been disconnected, then a gray-scale signal (i.e., data signal) that should have been supplied to the disconnected data electrode 122 is input through the input terminal 132 of the spare line 124.
In the data-to-counter-electrode type liquid crystal display device shown in FIGS. 15A through 15C, the input terminals 122A of the data electrodes 122 and the input terminal 132 of the spare line 124 are provided on the first substrate 120. On the other hand, a driver circuit (such as a driver IC) 128 to supply signals to the data electrodes 122 and the spare line 124 is formed on a flexible printed circuit board 126, which is provided separately from the first substrate 120, as shown in FIG. 15C. This flexible printed circuit board 126 and the first substrate 120 are bonded together by a tape automated bonding (TAB) technique.
As shown in FIGS. 15A and 16B, the spare line 124 crosses the data electrodes 122 at one end 122B of the data electrodes 122 with an insulating film 136 interposed between them. If any of the data electrodes 122 has been disconnected, a portion of the insulating film 136 at the intersection is burned off by a laser beam, thereby electrically connecting the disconnected data electrode 122 and the spare line 124 together. As a result, the data signal that should have been supplied to the disconnected data electrode 122 is input to the spare line 124. In this manner, the disconnected data electrode 122 can be repaired.
The two substrates 120 and 110 of this liquid crystal display device are bonded together with a seal member 139, including spacers 138, as shown in FIGS. 15C, 16A and 16B. A liquid crystal material 140 is injected into the gap between the two substrates 110 and 120. Also, the reference signal lines 118 and the gate lines 116 on the substrate 110 have input terminals 118A and input terminals 116A, respectively, which are connected to another driver circuit 130 as shown in FIG. 15C.
In the liquid crystal display device shown in FIGS. 15A through 16B, however, the spare line 124 is provided on the first substrate 120. Accordingly, a conductive film to be patterned into the spare line 124 and the insulating film 136 to electrically isolate the spare line 124 from the data electrodes 122 need to be additionally formed on the first substrate 120, thus complicating the manufacturing process and decreasing the yield potentially.
Also, the driver circuit 128 for controlling the data electrodes 122 and the spare line 124 is provided on the board 126 separately from the first substrate 120, and the board 126 needs to be bonded to the substrate 120 by the TAB technique, for example. Thus, this device has a complicated structure and might have an excessively large size.
Furthermore, the substrate 120 on which the input terminals 122A of the data electrodes 122 and the input terminal 132 of the spare line 124 are provided is different from the substrate 110 on which the input terminals 116A of the gate lines 116 and the input terminals 118A of the reference signal lines 118 are provided. Accordingly, the manufacturing process should include the process step of inverting the liquid crystal display device to bond the board 126 to the body of the device. In that case, the manufacturing cost might increase and its efficiency might decrease.
In order to overcome the problems described above, an object of the present invention is to provide a display device with a simplified structure and a disconnection-repairing spare line by a much more easy manufacturing process.
A display device according to a preferred embodiment of the present invention preferably includes: a first substrate; a second substrate, which is disposed so as to face the first substrate; and a display medium layer provided between the first and second substrates. The first substrate preferably includes striped data electrodes, a first group of connecting pads, and a second group of connecting pads. Each of the data electrodes preferably has a first end and a second end and preferably extends in a column direction. Each of the connecting pads in the first group is preferably connected electrically to the first end of associated one of the data electrodes. Each of the connecting pads in the second group is preferably connected electrically to the second end of associated one of the data electrodes. The second substrate preferably includes gate lines, reference signal lines, pixel electrodes, switching elements, data signal input terminals, a spare line, a third group of connecting pads, and a fourth group of connecting pads. The gate and reference signal lines preferably extend in a row direction. The pixel electrodes are preferably arranged in matrix. Each of the switching elements preferably has its ON/OFF states controlled by a voltage applied through associated one of the gate lines and is preferably provided between associated one of the reference signal lines and associated one of the pixel electrodes. Each of the data signal input terminals preferably receives a data signal to be supplied to associated one of the data electrodes. A data signal to be supplied to the data electrode may be passed through the spare line. The third group of connecting pads is preferably connected electrically to the data signal input terminals and is preferably provided so as to face the first group of connecting pads. The fourth group of connecting pads is preferably provided so as to face the second group of connecting pads and preferably crosses the spare line with an insulating layer interposed between them. Each of the connecting pads in the third group is preferably connected electrically to associated one of the connecting pads in the first group with an anisotropic conductive material. Each of the connecting pads in the fourth group is preferably connected electrically to associated one of the connecting pads in the second group with the anisotropic conductive material.
In one preferred embodiment of the present invention, a seal region is preferably provided between the periphery of the first substrate and the periphery of the second substrate. The first and second substrates are preferably bonded together with a seal member in the seal region. The seal member preferably includes the anisotropic conductive material. The first, second, third and fourth groups of connecting pads are preferably all located in the seal region.
In another preferred embodiment, the spare line may cross the third group of connecting pads with the insulating layer interposed between the spare line and the third group of connecting pads.
In still another preferred embodiment, the spare line may cross the fourth group of connecting pads inside of the seal region with the insulating layer interposed between the spare line and the fourth group of connecting pads.
In yet another preferred embodiment, the spare line may cross the third group of connecting pads inside of the seal region with the insulating layer interposed between the spare line and the third group of connecting pads.
In yet another preferred embodiment, the spare line may cross the fourth group of connecting pads outside of the seal region with the insulating layer interposed between the spare line and the fourth group of connecting pads.
In yet another preferred embodiment, the spare line may cross the third group of connecting pads outside of the seal region with the insulating layer interposed between the spare line and the third group of connecting pads.
In yet another preferred embodiment, each of the connecting pads in the fourth group preferably has a first portion with a first width and a second portion with a second width that is smaller than the first width. The second portion of each of the connecting pads in the fourth group preferably crosses the spare line.
In yet another preferred embodiment, each of the connecting pads in the third group preferably has a first portion with a first width and a second portion with a second width that is smaller than the first width. The second portion of each of the connecting pads in the third group preferably crosses the spare line.
In yet another preferred embodiment, the spare line preferably includes multiple branches that extend substantially vertically to the spare line itself. The branches of the spare line preferably cross the second portions of the connecting pads in the fourth group.
In yet another preferred embodiment, the spare line preferably includes multiple branches that extend substantially vertically to the spare line itself. The branches of the spare line preferably cross the second portions of the connecting pads in the third group.
In yet another preferred embodiment, each of the connecting pads in the fourth group may have multiple portions with the second width.
In yet another preferred embodiment, each of the connecting pads in the third group may have multiple portions with the second width.
In yet another preferred embodiment, each of the data electrodes is preferably combined with associated one of the connecting pads in the first group and with associated one of the connecting pads in the second group.
In yet another preferred embodiment, the display medium layer preferably includes a liquid crystal material or an organic EL material.
In yet another preferred embodiment, a portion of the insulating layer, which is located at an intersection between one of the connecting pads in the fourth group and the spare line, is preferably removed, thereby electrically connecting the connecting pad in the fourth group to the spare line.
In this particular preferred embodiment, another portion of the insulating layer, which is located at an intersection between one of the connecting pads in the third group and the spare line, is preferably removed, thereby electrically connecting the connecting pad in the third group to the spare line.
Another preferred embodiment of the present invention provides a method of repairing disconnected one of the data electrodes for the display device according to any of the preferred embodiments of the present invention described above. The method preferably includes the steps of: detecting the disconnected data electrode; and selectively removing a portion of the insulating layer, which is present at an intersection between one of the connecting pads, belonging to the fourth group and associated with the disconnected data electrode, and the spare line, thereby electrically connecting the connecting pad in the fourth group to the spare line.
In one preferred embodiment of the present invention, the method preferably further includes the step of selectively removing another portion of the insulating layer, which is present at an intersection between one of the connecting pads, belonging to the third group and associated with the disconnected data electrode, and the spare line, thereby electrically connecting the connecting pad in the third group to the spare line.
Other features, elements, processes, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.